Copyright (c) 1994-1996, 1998-2005, 2007-2008 Todd C. Miller <Todd.Miller@courtesan.com> Permission to use, copy, modify, and distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Sponsored in part by the Defense Advanced Research Projects Agency (DARPA) and Air Force Research Laboratory, Air Force Materiel Command, USAF, under agreement number F39502-99-1-0512. $Sudo: sudoers.pod,v 1.155 2008/12/03 20:57:13 millert Exp $ =pod =head1 NAME sudoers - list of which users may execute what =head1 DESCRIPTION The I<sudoers> file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what). When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match). The I<sudoers> grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you don't know what EBNF is; it is fairly simple, and the definitions below are annotated. =head2 Quick guide to EBNF EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up of I<production rules>. E.g., symbol ::= definition | alternate1 | alternate2 ... Each I<production rule> references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with "wildcard" characters, which have different meanings. =over 4 =item C<?> Means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or not at all. =item C<*> Means that the preceding symbol (or group of symbols) may appear zero or more times. =item C<+> Means that the preceding symbol (or group of symbols) may appear one or more times. =back Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name). =head2 Aliases There are four kinds of aliases: C<User_Alias>, C<Runas_Alias>, C<Host_Alias> and C<Cmnd_Alias>. Alias ::= 'User_Alias' User_Alias (':' User_Alias)* | 'Runas_Alias' Runas_Alias (':' Runas_Alias)* | 'Host_Alias' Host_Alias (':' Host_Alias)* | 'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)* User_Alias ::= NAME '=' User_List Runas_Alias ::= NAME '=' Runas_List Host_Alias ::= NAME '=' Host_List Cmnd_Alias ::= NAME '=' Cmnd_List NAME ::= [A-Z]([A-Z][0-9]_)* Each I<alias> definition is of the form Alias_Type NAME = item1, item2, ... where I<Alias_Type> is one of C<User_Alias>, C<Runas_Alias>, C<Host_Alias>, or C<Cmnd_Alias>. A C<NAME> is a string of uppercase letters, numbers, and underscore characters ('_'). A C<NAME> B<must> start with an uppercase letter. It is possible to put several alias definitions of the same type on a single line, joined by a colon (':'). E.g., Alias_Type NAME = item1, item2, item3 : NAME = item4, item5 The definitions of what constitutes a valid I<alias> member follow. User_List ::= User | User ',' User_List User ::= '!'* username | '!'* '#'uid | '!'* '%'group | '!'* '+'netgroup | '!'* User_Alias A C<User_List> is made up of one or more usernames, uids (prefixed with '#'), system groups (prefixed with '%'), netgroups (prefixed with '+') and C<User_Alias>es. Each list item may be prefixed with zero or more '!' operators. An odd number of '!' operators negate the value of the item; an even number just cancel each other out. Runas_List ::= Runas_Member | Runas_Member ',' Runas_List Runas_Member ::= '!'* username | '!'* '#'uid | '!'* '%'group | '!'* +netgroup | '!'* Runas_Alias A C<Runas_List> is similar to a C<User_List> except that instead of C<User_Alias>es it can contain C<Runas_Alias>es. Note that usernames and groups are matched as strings. In other words, two users (groups) with the same uid (gid) are considered to be distinct. If you wish to match all usernames with the same uid (e.g.E<nbsp>root and toor), you can use a uid instead (#0 in the example given). Host_List ::= Host | Host ',' Host_List Host ::= '!'* hostname | '!'* ip_addr | '!'* network(/netmask)? | '!'* '+'netgroup | '!'* Host_Alias A C<Host_List> is made up of one or more hostnames, IP addresses, network numbers, netgroups (prefixed with '+') and other aliases. Again, the value of an item may be negated with the '!' operator. If you do not specify a netmask along with the network number, B<sudo> will query each of the local host's network interfaces and, if the network number corresponds to one of the hosts's network interfaces, the corresponding netmask will be used. The netmask may be specified either in standard IP address notation (e.g.E<nbsp>255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g.E<nbsp>24 or 64). A hostname may include shell-style wildcards (see the L<Wildcards> section below), but unless the C<hostname> command on your machine returns the fully qualified hostname, you'll need to use the I<fqdn> option for wildcards to be useful. Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List commandname ::= filename | filename args | filename '""' Cmnd ::= '!'* commandname | '!'* directory | '!'* "sudoedit" | '!'* Cmnd_Alias A C<Cmnd_List> is a list of one or more commandnames, directories, and other aliases. A commandname is a fully qualified filename which may include shell-style wildcards (see the L<Wildcards> section below). A simple filename allows the user to run the command with any arguments he/she wishes. However, you may also specify command line arguments (including wildcards). Alternately, you can specify C<""> to indicate that the command may only be run B<without> command line arguments. A directory is a fully qualified pathname ending in a '/'. When you specify a directory in a C<Cmnd_List>, the user will be able to run any file within that directory (but not in any subdirectories therein). If a C<Cmnd> has associated command line arguments, then the arguments in the C<Cmnd> must match exactly those given by the user on the command line (or match the wildcards if there are any). Note that the following characters must be escaped with a '\' if they are used in command arguments: ',', ':', '=', '\'. The special command C<"sudoedit"> is used to permit a user to run B<sudo> with the B<-e> option (or as B<sudoedit>). It may take command line arguments just as a normal command does. =head2 Defaults Certain configuration options may be changed from their default values at runtime via one or more C<Default_Entry> lines. These may affect all users on any host, all users on a specific host, a specific user, a specific command, or commands being run as a specific user. Note that per-command entries may not include command line arguments. If you need to specify arguments, define a C<Cmnd_Alias> and reference that instead. Default_Type ::= 'Defaults' | 'Defaults' '@' Host_List | 'Defaults' ':' User_List | 'Defaults' '!' Cmnd_List | 'Defaults' '>' Runas_List Default_Entry ::= Default_Type Parameter_List Parameter_List ::= Parameter | Parameter ',' Parameter_List Parameter ::= Parameter '=' Value | Parameter '+=' Value | Parameter '-=' Value | '!'* Parameter Parameters may be B<flags>, B<integer> values, B<strings>, or B<lists>. Flags are implicitly boolean and can be turned off via the '!' operator. Some integer, string and list parameters may also be used in a boolean context to disable them. Values may be enclosed in double quotes (C<">) when they contain multiple words. Special characters may be escaped with a backslash (C<\>). Lists have two additional assignment operators, C<+=> and C<-=>. These operators are used to add to and delete from a list respectively. It is not an error to use the C<-=> operator to remove an element that does not exist in a list. Defaults entries are parsed in the following order: generic, host and user Defaults first, then runas Defaults and finally command defaults. See L</"SUDOERS OPTIONS"> for a list of supported Defaults parameters. =head2 User Specification User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \ (':' Host_List '=' Cmnd_Spec_List)* Cmnd_Spec_List ::= Cmnd_Spec | Cmnd_Spec ',' Cmnd_Spec_List Cmnd_Spec ::= Runas_Spec? Tag_Spec* Cmnd Runas_Spec ::= '(' Runas_List? (: Runas_List)? ')' Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' | 'SETENV:' | 'NOSETENV:' ) A B<user specification> determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as B<root>, but this can be changed on a per-command basis. Let's break that down into its constituent parts: =head2 Runas_Spec A C<Runas_Spec> determines the user and/or the group that a command may be run as. A fully-specified C<Runas_Spec> consists of two C<Runas_List>s (as defined above) separated by a colon (':') and enclosed in a set of parentheses. The first C<Runas_List> indicates which users the command may be run as via B<sudo>'s B<-u> option. The second defines a list of groups that can be specified via B<sudo>'s B<-g> option. If both C<Runas_List>s are specified, the command may be run with any combination of users and groups listed in their respective C<Runas_List>s. If only the first is specified, the command may be run as any user in the list but no B<-g> option may be specified. If the first C<Runas_List> is empty but the second is specified, the command may be run as the invoking user with the group set to any listed in the C<Runas_List>. If no C<Runas_Spec> is specified the command may be run as B<root> and no group may be specified. A C<Runas_Spec> sets the default for the commands that follow it. What this means is that for the entry: dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm The user B<dgb> may run F</bin/ls>, F</bin/kill>, and F</usr/bin/lprm> -- but only as B<operator>. E.g., $ sudo -u operator /bin/ls. It is also possible to override a C<Runas_Spec> later on in an entry. If we modify the entry like so: dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm Then user B<dgb> is now allowed to run F</bin/ls> as B<operator>, but F</bin/kill> and F</usr/bin/lprm> as B<root>. We can extend this to allow B<dgb> to run C</bin/ls> with either the user or group set to B<operator>: dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill, \ /usr/bin/lprm In the following example, user B<tcm> may run commands that access a modem device file with the dialer group. Note that in this example only the group will be set, the command still runs as user B<tcm>. tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu, \ /usr/local/bin/minicom =head2 Tag_Spec A command may have zero or more tags associated with it. There are eight possible tag values, C<NOPASSWD>, C<PASSWD>, C<NOEXEC>, C<EXEC>, C<SETENV> and C<NOSETENV>. Once a tag is set on a C<Cmnd>, subsequent C<Cmnd>s in the C<Cmnd_Spec_List>, inherit the tag unless it is overridden by the opposite tag (i.e.: C<PASSWD> overrides C<NOPASSWD> and C<NOEXEC> overrides C<EXEC>). =head3 NOPASSWD and PASSWD By default, B<sudo> requires that a user authenticate him or herself before running a command. This behavior can be modified via the C<NOPASSWD> tag. Like a C<Runas_Spec>, the C<NOPASSWD> tag sets a default for the commands that follow it in the C<Cmnd_Spec_List>. Conversely, the C<PASSWD> tag can be used to reverse things. For example: ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm would allow the user B<ray> to run F</bin/kill>, F</bin/ls>, and F</usr/bin/lprm> as B<root> on the machine rushmore without authenticating himself. If we only want B<ray> to be able to run F</bin/kill> without a password the entry would be: ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm Note, however, that the C<PASSWD> tag has no effect on users who are in the group specified by the I<exempt_group> option. By default, if the C<NOPASSWD> tag is applied to any of the entries for a user on the current host, he or she will be able to run C<sudo -l> without a password. Additionally, a user may only run C<sudo -v> without a password if the C<NOPASSWD> tag is present for all a user's entries that pertain to the current host. This behavior may be overridden via the verifypw and listpw options. =head3 NOEXEC and EXEC If B<sudo> has been compiled with I<noexec> support and the underlying operating system supports it, the C<NOEXEC> tag can be used to prevent a dynamically-linked executable from running further commands itself. In the following example, user B<aaron> may run F</usr/bin/more> and F</usr/bin/vi> but shell escapes will be disabled. aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi See the L<PREVENTING SHELL ESCAPES> section below for more details on how C<NOEXEC> works and whether or not it will work on your system. =head3 SETENV and NOSETENV These tags override the value of the I<setenv> option on a per-command basis. Note that if C<SETENV> has been set for a command, any environment variables set on the command line way are not subject to the restrictions imposed by I<env_check>, I<env_delete>, or I<env_keep>. As such, only trusted users should be allowed to set variables in this manner. If the command matched is B<ALL>, the C<SETENV> tag is implied for that command; this default may be overridden by use of the C<UNSETENV> tag. =head2 Wildcards B<sudo> allows shell-style I<wildcards> (aka meta or glob characters) to be used in hostnames, pathnames and command line arguments in the I<sudoers> file. Wildcard matching is done via the B<POSIX> L<fnmatch(3)> routine. Note that these are I<not> regular expressions. =over 8 =item C<*> Matches any set of zero or more characters. =item C<?> Matches any single character. =item C<[...]> Matches any character in the specified range. =item C<[!...]> Matches any character B<not> in the specified range. =item C<\x> For any character "x", evaluates to "x". This is used to escape special characters such as: "*", "?", "[", and "}". =back POSIX character classes may also be used if your system's L<fnmatch(3)> function supports them. However, because the C<':'> character has special meaning in I<sudoers>, it must be escaped. For example: /bin/ls [[\:alpha\:]]* Would match any filename beginning with a letter. Note that a forward slash ('/') will B<not> be matched by wildcards used in the pathname. When matching the command line arguments, however, a slash B<does> get matched by wildcards. This is to make a path like: /usr/bin/* match F</usr/bin/who> but not F</usr/bin/X11/xterm>. =head2 Exceptions to wildcard rules The following exceptions apply to the above rules: =over 8 =item C<""> If the empty string C<""> is the only command line argument in the I<sudoers> entry it means that command is not allowed to be run with B<any> arguments. =back =head2 Including other files from within sudoers It is possible to include other I<sudoers> files from within the I<sudoers> file currently being parsed using the C<#include> directive, similar to the one used by the C preprocessor. This is useful, for example, for keeping a site-wide I<sudoers> file in addition to a per-machine local one. For the sake of this example the site-wide I<sudoers> will be F</etc/sudoers> and the per-machine one will be F</etc/sudoers.local>. To include F</etc/sudoers.local> from F</etc/sudoers> we would use the following line in F</etc/sudoers>: #include /etc/sudoers.local When B<sudo> reaches this line it will suspend processing of the current file (F</etc/sudoers>) and switch to F</etc/sudoers.local>. Upon reaching the end of F</etc/sudoers.local>, the rest of F</etc/sudoers> will be processed. Files that are included may themselves include other files. A hard limit of 128 nested include files is enforced to prevent include file loops. =head2 Other special characters and reserved words The pound sign ('#') is used to indicate a comment (unless it is part of a #include directive or unless it occurs in the context of a user name and is followed by one or more digits, in which case it is treated as a uid). Both the comment character and any text after it, up to the end of the line, are ignored. The reserved word B<ALL> is a built-in I<alias> that always causes a match to succeed. It can be used wherever one might otherwise use a C<Cmnd_Alias>, C<User_Alias>, C<Runas_Alias>, or C<Host_Alias>. You should not try to define your own I<alias> called B<ALL> as the built-in alias will be used in preference to your own. Please note that using B<ALL> can be dangerous since in a command context, it allows the user to run B<any> command on the system. An exclamation point ('!') can be used as a logical I<not> operator both in an I<alias> and in front of a C<Cmnd>. This allows one to exclude certain values. Note, however, that using a C<!> in conjunction with the built-in C<ALL> alias to allow a user to run "all but a few" commands rarely works as intended (see SECURITY NOTES below). Long lines can be continued with a backslash ('\') as the last character on the line. Whitespace between elements in a list as well as special syntactic characters in a I<User Specification> ('=', ':', '(', ')') is optional. The following characters must be escaped with a backslash ('\') when used as part of a word (e.g.E<nbsp>a username or hostname): '@', '!', '=', ':', ',', '(', ')', '\'. =head1 SUDOERS OPTIONS B<sudo>'s behavior can be modified by C<Default_Entry> lines, as explained earlier. A list of all supported Defaults parameters, grouped by type, are listed below. B<Flags>: =over 16 =item always_set_home If set, B<sudo> will set the C<HOME> environment variable to the home directory of the target user (which is root unless the B<-u> option is used). This effectively means that the B<-H> option is always implied. This flag is I<off> by default. =item authenticate If set, users must authenticate themselves via a password (or other means of authentication) before they may run commands. This default may be overridden via the C<PASSWD> and C<NOPASSWD> tags. This flag is I<on> by default. =item closefrom_override If set, the user may use B<sudo>'s B<-C> option which overrides the default starting point at which B<sudo> begins closing open file descriptors. This flag is I<off> by default. =item env_editor If set, B<visudo> will use the value of the EDITOR or VISUAL environment variables before falling back on the default editor list. Note that this may create a security hole as it allows the user to run any arbitrary command as root without logging. A safer alternative is to place a colon-separated list of editors in the C<editor> variable. B<visudo> will then only use the EDITOR or VISUAL if they match a value specified in C<editor>. This flag is I<@env_editor@> by default. =item env_reset If set, B<sudo> will reset the environment to only contain the LOGNAME, SHELL, USER, USERNAME and the C<SUDO_*> variables. Any variables in the caller's environment that match the C<env_keep> and C<env_check> lists are then added. The default contents of the C<env_keep> and C<env_check> lists are displayed when B<sudo> is run by root with the I<-V> option. If the I<secure_path> option is set, its value will be used for the C<PATH> environment variable. This flag is I<on> by default. =item fqdn Set this flag if you want to put fully qualified hostnames in the I<sudoers> file. I.e., instead of myhost you would use myhost.mydomain.edu. You may still use the short form if you wish (and even mix the two). Beware that turning on I<fqdn> requires B<sudo> to make DNS lookups which may make B<sudo> unusable if DNS stops working (for example if the machine is not plugged into the network). Also note that you must use the host's official name as DNS knows it. That is, you may not use a host alias (C<CNAME> entry) due to performance issues and the fact that there is no way to get all aliases from DNS. If your machine's hostname (as returned by the C<hostname> command) is already fully qualified you shouldn't need to set I<fqdn>. This flag is I<@fqdn@> by default. =item ignore_dot If set, B<sudo> will ignore '.' or '' (current dir) in the C<PATH> environment variable; the C<PATH> itself is not modified. This flag is I<@ignore_dot@> by default. =item ignore_local_sudoers If set via LDAP, parsing of F<@sysconfdir@/sudoers> will be skipped. This is intended for Enterprises that wish to prevent the usage of local sudoers files so that only LDAP is used. This thwarts the efforts of rogue operators who would attempt to add roles to F<@sysconfdir@/sudoers>. When this option is present, F<@sysconfdir@/sudoers> does not even need to exist. Since this option tells B<sudo> how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for the C<cn=defaults> section. This flag is I<off> by default. =item insults If set, B<sudo> will insult users when they enter an incorrect password. This flag is I<@insults@> by default. =item log_host If set, the hostname will be logged in the (non-syslog) B<sudo> log file. This flag is I<off> by default. =item log_year If set, the four-digit year will be logged in the (non-syslog) B<sudo> log file. This flag is I<off> by default. =item long_otp_prompt When validating with a One Time Password (OPT) scheme such as B<S/Key> or B<OPIE>, a two-line prompt is used to make it easier to cut and paste the challenge to a local window. It's not as pretty as the default but some people find it more convenient. This flag is I<@long_otp_prompt@> by default. =item mail_always Send mail to the I<mailto> user every time a users runs B<sudo>. This flag is I<off> by default. =item mail_badpass Send mail to the I<mailto> user if the user running B<sudo> does not enter the correct password. This flag is I<off> by default. =item mail_no_host If set, mail will be sent to the I<mailto> user if the invoking user exists in the I<sudoers> file, but is not allowed to run commands on the current host. This flag is I<@mail_no_host@> by default. =item mail_no_perms If set, mail will be sent to the I<mailto> user if the invoking user is allowed to use B<sudo> but the command they are trying is not listed in their I<sudoers> file entry or is explicitly denied. This flag is I<@mail_no_perms@> by default. =item mail_no_user If set, mail will be sent to the I<mailto> user if the invoking user is not in the I<sudoers> file. This flag is I<@mail_no_user@> by default. =item noexec If set, all commands run via B<sudo> will behave as if the C<NOEXEC> tag has been set, unless overridden by a C<EXEC> tag. See the description of I<NOEXEC and EXEC> below as well as the L<PREVENTING SHELL ESCAPES> section at the end of this manual. This flag is I<off> by default. =item path_info Normally, B<sudo> will tell the user when a command could not be found in their C<PATH> environment variable. Some sites may wish to disable this as it could be used to gather information on the location of executables that the normal user does not have access to. The disadvantage is that if the executable is simply not in the user's C<PATH>, B<sudo> will tell the user that they are not allowed to run it, which can be confusing. This flag is I<@path_info@> by default. =item passprompt_override The password prompt specified by I<passprompt> will normally only be used if the passwod prompt provided by systems such as PAM matches the string "Password:". If I<passprompt_override> is set, I<passprompt> will always be used. This flag is I<off> by default. =item preserve_groups By default B<sudo> will initialize the group vector to the list of groups the target user is in. When I<preserve_groups> is set, the user's existing group vector is left unaltered. The real and effective group IDs, however, are still set to match the target user. This flag is I<off> by default. =item requiretty If set, B<sudo> will only run when the user is logged in to a real tty. When this flag is set, B<sudo> can only be run from a login session and not via other means such as L<cron(8)> or cgi-bin scripts. This flag is I<off> by default. =item root_sudo If set, root is allowed to run B<sudo> too. Disabling this prevents users from "chaining" B<sudo> commands to get a root shell by doing something like C<"sudo sudo /bin/sh">. Note, however, that turning off I<root_sudo> will also prevent root and from running B<sudoedit>. Disabling I<root_sudo> provides no real additional security; it exists purely for historical reasons. This flag is I<@root_sudo@> by default. =item rootpw If set, B<sudo> will prompt for the root password instead of the password of the invoking user. This flag is I<off> by default. =item runaspw If set, B<sudo> will prompt for the password of the user defined by the I<runas_default> option (defaults to C<@runas_default@>) instead of the password of the invoking user. This flag is I<off> by default. =item set_home If set and B<sudo> is invoked with the B<-s> option the C<HOME> environment variable will be set to the home directory of the target user (which is root unless the B<-u> option is used). This effectively makes the B<-s> option imply B<-H>. This flag is I<off> by default. =item set_logname Normally, B<sudo> will set the C<LOGNAME>, C<USER> and C<USERNAME> environment variables to the name of the target user (usually root unless the B<-u> option is given). However, since some programs (including the RCS revision control system) use C<LOGNAME> to determine the real identity of the user, it may be desirable to change this behavior. This can be done by negating the set_logname option. Note that if the I<env_reset> option has not been disabled, entries in the I<env_keep> list will override the value of I<set_logname>. This flag is I<off> by default. =item setenv Allow the user to disable the I<env_reset> option from the command line. Additionally, environment variables set via the command line are not subject to the restrictions imposed by I<env_check>, I<env_delete>, or I<env_keep>. As such, only trusted users should be allowed to set variables in this manner. This flag is I<off> by default. =item shell_noargs If set and B<sudo> is invoked with no arguments it acts as if the B<-s> option had been given. That is, it runs a shell as root (the shell is determined by the C<SHELL> environment variable if it is set, falling back on the shell listed in the invoking user's /etc/passwd entry if not). This flag is I<off> by default. =item stay_setuid Normally, when B<sudo> executes a command the real and effective UIDs are set to the target user (root by default). This option changes that behavior such that the real UID is left as the invoking user's UID. In other words, this makes B<sudo> act as a setuid wrapper. This can be useful on systems that disable some potentially dangerous functionality when a program is run setuid. This option is only effective on systems with either the setreuid() or setresuid() function. This flag is I<off> by default. =item targetpw If set, B<sudo> will prompt for the password of the user specified by the B<-u> option (defaults to C<root>) instead of the password of the invoking user. Note that this precludes the use of a uid not listed in the passwd database as an argument to the B<-u> option. This flag is I<off> by default. =item tty_tickets If set, users must authenticate on a per-tty basis. Normally, B<sudo> uses a directory in the ticket dir with the same name as the user running it. With this flag enabled, B<sudo> will use a file named for the tty the user is logged in on in that directory. This flag is I<@tty_tickets@> by default. =item use_loginclass If set, B<sudo> will apply the defaults specified for the target user's login class if one exists. Only available if B<sudo> is configured with the --with-logincap option. This flag is I<off> by default. =item visiblepw By default, B<sudo> will refuse to run if the user must enter a password but it is not possible to disable echo on the terminal. If the I<visiblepw> flag is set, B<sudo> will prompt for a password even when it would be visible on the screen. This makes it possible to run things like C<"rsh somehost sudo ls"> since L<rsh(1)> does not allocate a tty. This flag is I<off> by default. =back B<Integers>: =over 16 =item closefrom Before it executes a command, B<sudo> will close all open file descriptors other than standard input, standard output and standard error (ie: file descriptors 0-2). The I<closefrom> option can be used to specify a different file descriptor at which to start closing. The default is C<3>. =item passwd_tries The number of tries a user gets to enter his/her password before B<sudo> logs the failure and exits. The default is C<@passwd_tries@>. =back B<Integers that can be used in a boolean context>: =over 16 =item loglinelen Number of characters per line for the file log. This value is used to decide when to wrap lines for nicer log files. This has no effect on the syslog log file, only the file log. The default is C<@loglen@> (use 0 or negate the option to disable word wrap). =item passwd_timeout Number of minutes before the B<sudo> password prompt times out. The default is C<@password_timeout@>; set this to C<0> for no password timeout. =item timestamp_timeout Number of minutes that can elapse before B<sudo> will ask for a passwd again. The default is C<@timeout@>. Set this to C<0> to always prompt for a password. If set to a value less than C<0> the user's timestamp will never expire. This can be used to allow users to create or delete their own timestamps via C<sudo -v> and C<sudo -k> respectively. =item umask Umask to use when running the command. Negate this option or set it to 0777 to preserve the user's umask. The actual umask that is used will be the union of the user's umask and C<@sudo_umask@>. This guarantees that B<sudo> never lowers the umask when running a command. Note on systems that use PAM, the default PAM configuration may specify its own umask which will override the value set in I<sudoers>. =back B<Strings>: =over 16 =item badpass_message Message that is displayed if a user enters an incorrect password. The default is C<@badpass_message@> unless insults are enabled. =item editor A colon (':') separated list of editors allowed to be used with B<visudo>. B<visudo> will choose the editor that matches the user's EDITOR environment variable if possible, or the first editor in the list that exists and is executable. The default is the path to vi on your system. =item mailsub Subject of the mail sent to the I<mailto> user. The escape C<%h> will expand to the hostname of the machine. Default is C<@mailsub@>. =item noexec_file Path to a shared library containing dummy versions of the execv(), execve() and fexecve() library functions that just return an error. This is used to implement the I<noexec> functionality on systems that support C<LD_PRELOAD> or its equivalent. Defaults to F<@noexec_file@>. =item passprompt The default prompt to use when asking for a password; can be overridden via the B<-p> option or the C<SUDO_PROMPT> environment variable. The following percent (`C<%>') escapes are supported: =over 4 =item C<%H> expanded to the local hostname including the domain name (on if the machine's hostname is fully qualified or the I<fqdn> option is set) =item C<%h> expanded to the local hostname without the domain name =item C<%p> expanded to the user whose password is being asked for (respects the I<rootpw>, I<targetpw> and I<runaspw> flags in I<sudoers>) =item C<%U> expanded to the login name of the user the command will be run as (defaults to root) =item C<%u> expanded to the invoking user's login name =item C<%%> two consecutive C<%> characters are collapsed into a single C<%> character =back The default value is C<@passprompt@>. =item role The default SELinux role to use when constructing a new security context to run the command. The default role may be overridden on a per-command basis in I<sudoers> or via command line options. This option is only available whe B<sudo> is built with SELinux support. =item runas_default The default user to run commands as if the B<-u> option is not specified on the command line. This defaults to C<@runas_default@>. Note that if I<runas_default> is set it B<must> occur before any C<Runas_Alias> specifications. =item syslog_badpri Syslog priority to use when user authenticates unsuccessfully. Defaults to C<@badpri@>. =item syslog_goodpri Syslog priority to use when user authenticates successfully. Defaults to C<@goodpri@>. =item sudoers_locale Locale to use when parsing the sudoers file. Note that changing the locale may affect how sudoers is interpreted. Defaults to C<"C">. =item timestampdir The directory in which B<sudo> stores its timestamp files. The default is F<@timedir@>. =item timestampowner The owner of the timestamp directory and the timestamps stored therein. The default is C<root>. =item type The default SELinux type to use when constructing a new security context to run the command. The default type may be overridden on a per-command basis in I<sudoers> or via command line options. This option is only available whe B<sudo> is built with SELinux support. =back B<Strings that can be used in a boolean context>: =over 12 =item askpass The I<askpass> option specifies the fully qualified path to a helper program used to read the user's password when no terminal is available. This may be the case when B<sudo> is executed from a graphical (as opposed to text-based) application. The program specified by I<askpass> should display the argument passed to it as the prompt and write the user's password to the standard output. The value of I<askpass> may be overridden by the C<SUDO_ASKPASS> environment variable. =item env_file The I<env_file> options specifies the fully qualified path to a file containing variables to be set in the environment of the program being run. Entries in this file should be of the form C<VARIABLE=value>. Variables in this file are subject to other B<sudo> environment settings such as I<env_keep> and I<env_check>. =item exempt_group Users in this group are exempt from password and PATH requirements. This is not set by default. =item lecture This option controls when a short lecture will be printed along with the password prompt. It has the following possible values: =over 8 =item always Always lecture the user. =item never Never lecture the user. =item once Only lecture the user the first time they run B<sudo>. =back If no value is specified, a value of I<once> is implied. Negating the option results in a value of I<never> being used. The default value is I<@lecture@>. =item lecture_file Path to a file containing an alternate B<sudo> lecture that will be used in place of the standard lecture if the named file exists. By default, B<sudo> uses a built-in lecture. =item listpw This option controls when a password will be required when a user runs B<sudo> with the B<-l> option. It has the following possible values: =over 8 =item all All the user's I<sudoers> entries for the current host must have the C<NOPASSWD> flag set to avoid entering a password. =item always The user must always enter a password to use the B<-l> option. =item any At least one of the user's I<sudoers> entries for the current host must have the C<NOPASSWD> flag set to avoid entering a password. =item never The user need never enter a password to use the B<-l> option. =back If no value is specified, a value of I<any> is implied. Negating the option results in a value of I<never> being used. The default value is I<any>. =item logfile Path to the B<sudo> log file (not the syslog log file). Setting a path turns on logging to a file; negating this option turns it off. By default, B<sudo> logs via syslog. =item mailerflags Flags to use when invoking mailer. Defaults to B<-t>. =item mailerpath Path to mail program used to send warning mail. Defaults to the path to sendmail found at configure time. =item mailfrom Address to use for the "from" address when sending warning and error mail. The address should be enclosed in double quotes (C<">) to protect against B<sudo> interpreting the C<@> sign. Defaults to the name of the user running B<sudo>. =item mailto Address to send warning and error mail to. The address should be enclosed in double quotes (C<">) to protect against B<sudo> interpreting the C<@> sign. Defaults to C<@mailto@>. =item secure_path Path used for every command run from B<sudo>. If you don't trust the people running B<sudo> to have a sane C<PATH> environment variable you may want to use this. Another use is if you want to have the "root path" be separate from the "user path." Users in the group specified by the I<exempt_group> option are not affected by I<secure_path>. This is not set by default. =item syslog Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to C<@logfac@>. =item verifypw This option controls when a password will be required when a user runs B<sudo> with the B<-v> option. It has the following possible values: =over 8 =item all All the user's I<sudoers> entries for the current host must have the C<NOPASSWD> flag set to avoid entering a password. =item always The user must always enter a password to use the B<-v> option. =item any At least one of the user's I<sudoers> entries for the current host must have the C<NOPASSWD> flag set to avoid entering a password. =item never The user need never enter a password to use the B<-v> option. =back If no value is specified, a value of I<all> is implied. Negating the option results in a value of I<never> being used. The default value is I<all>. =back B<Lists that can be used in a boolean context>: =over 16 =item env_check Environment variables to be removed from the user's environment if the variable's value contains C<%> or C</> characters. This can be used to guard against printf-style format vulnerabilities in poorly-written programs. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the C<=>, C<+=>, C<-=>, and C<!> operators respectively. Regardless of whether the C<env_reset> option is enabled or disabled, variables specified by C<env_check> will be preserved in the environment if they pass the aforementioned check. The default list of environment variables to check is displayed when B<sudo> is run by root with the I<-V> option. =item env_delete Environment variables to be removed from the user's environment. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the C<=>, C<+=>, C<-=>, and C<!> operators respectively. The default list of environment variables to remove is displayed when B<sudo> is run by root with the I<-V> option. Note that many operating systems will remove potentially dangerous variables from the environment of any setuid process (such as B<sudo>). =item env_keep Environment variables to be preserved in the user's environment when the I<env_reset> option is in effect. This allows fine-grained control over the environment B<sudo>-spawned processes will receive. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the C<=>, C<+=>, C<-=>, and C<!> operators respectively. The default list of variables to keep is displayed when B<sudo> is run by root with the I<-V> option. =back When logging via L<syslog(3)>, B<sudo> accepts the following values for the syslog facility (the value of the B<syslog> Parameter): B<authpriv> (if your OS supports it), B<auth>, B<daemon>, B<user>, B<local0>, B<local1>, B<local2>, B<local3>, B<local4>, B<local5>, B<local6>, and B<local7>. The following syslog priorities are supported: B<alert>, B<crit>, B<debug>, B<emerg>, B<err>, B<info>, B<notice>, and B<warning>. =head1 FILES =over 24 =item F<@sysconfdir@/sudoers> List of who can run what =item F</etc/group> Local groups file =item F</etc/netgroup> List of network groups =back =head1 EXAMPLES Below are example I<sudoers> entries. Admittedly, some of these are a bit contrived. First, we define our I<aliases>: # User alias specification User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBMASTERS = will, wendy, wim # Runas alias specification Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase # Host alias specification Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 126.96.36.199/255.255.0.0 Host_Alias CSNETS = 188.8.131.52, 184.108.40.206/24, 220.127.116.11 Host_Alias SERVERS = master, mail, www, ns Host_Alias CDROM = orion, perseus, hercules # Cmnd alias specification Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \ /usr/local/bin/tcsh, /usr/bin/rsh, \ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less Here we override some of the compiled in default values. We want B<sudo> to log via L<syslog(3)> using the I<auth> facility in all cases. We don't want to subject the full time staff to the B<sudo> lecture, user B<millert> need not give a password, and we don't want to reset the C<LOGNAME>, C<USER> or C<USERNAME> environment variables when running commands as root. Additionally, on the machines in the I<SERVERS> C<Host_Alias>, we keep an additional local log file and make sure we log the year in each log line since the log entries will be kept around for several years. Lastly, we disable shell escapes for the commands in the PAGERS C<Cmnd_Alias> (F</usr/bin/more>, F</usr/bin/pg> and F</usr/bin/less>). # Override built-in defaults Defaults syslog=auth Defaults>root !set_logname Defaults:FULLTIMERS !lecture Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec The I<User specification> is the part that actually determines who may run what. root ALL = (ALL) ALL %wheel ALL = (ALL) ALL We let B<root> and any user in group B<wheel> run any command on any host as any user. FULLTIMERS ALL = NOPASSWD: ALL Full time sysadmins (B<millert>, B<mikef>, and B<dowdy>) may run any command on any host without authenticating themselves. PARTTIMERS ALL = ALL Part time sysadmins (B<bostley>, B<jwfox>, and B<crawl>) may run any command on any host but they must authenticate themselves first (since the entry lacks the C<NOPASSWD> tag). jack CSNETS = ALL The user B<jack> may run any command on the machines in the I<CSNETS> alias (the networks C<18.104.22.168>, C<22.214.171.124>, and C<126.96.36.199>). Of those networks, only C<188.8.131.52> has an explicit netmask (in CIDR notation) indicating it is a class C network. For the other networks in I<CSNETS>, the local machine's netmask will be used during matching. lisa CUNETS = ALL The user B<lisa> may run any command on any host in the I<CUNETS> alias (the class B network C<184.108.40.206>). operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/ The B<operator> user may run commands limited to simple maintenance. Here, those are commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the directory F</usr/oper/bin/>. joe ALL = /usr/bin/su operator The user B<joe> may only L<su(1)> to operator. pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root The user B<pete> is allowed to change anyone's password except for root on the I<HPPA> machines. Note that this assumes L<passwd(1)> does not take multiple usernames on the command line. bob SPARC = (OP) ALL : SGI = (OP) ALL The user B<bob> may run anything on the I<SPARC> and I<SGI> machines as any user listed in the I<OP> C<Runas_Alias> (B<root> and B<operator>). jim +biglab = ALL The user B<jim> may run any command on machines in the I<biglab> netgroup. B<sudo> knows that "biglab" is a netgroup due to the '+' prefix. +secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser Users in the B<secretaries> netgroup need to help manage the printers as well as add and remove users, so they are allowed to run those commands on all machines. fred ALL = (DB) NOPASSWD: ALL The user B<fred> can run commands as any user in the I<DB> C<Runas_Alias> (B<oracle> or B<sybase>) without giving a password. john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root* On the I<ALPHA> machines, user B<john> may su to anyone except root but he is not allowed to specify any options to the L<su(1)> command. jen ALL, !SERVERS = ALL The user B<jen> may run any command on any machine except for those in the I<SERVERS> C<Host_Alias> (master, mail, www and ns). jill SERVERS = /usr/bin/, !SU, !SHELLS For any machine in the I<SERVERS> C<Host_Alias>, B<jill> may run any commands in the directory F</usr/bin/> except for those commands belonging to the I<SU> and I<SHELLS> C<Cmnd_Aliases>. steve CSNETS = (operator) /usr/local/op_commands/ The user B<steve> may run any command in the directory /usr/local/op_commands/ but only as user operator. matt valkyrie = KILL On his personal workstation, valkyrie, B<matt> needs to be able to kill hung processes. WEBMASTERS www = (www) ALL, (root) /usr/bin/su www On the host www, any user in the I<WEBMASTERS> C<User_Alias> (will, wendy, and wim), may run any command as user www (which owns the web pages) or simply L<su(1)> to www. ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM Any user may mount or unmount a CD-ROM on the machines in the CDROM C<Host_Alias> (orion, perseus, hercules) without entering a password. This is a bit tedious for users to type, so it is a prime candidate for encapsulating in a shell script. =head1 SECURITY NOTES It is generally not effective to "subtract" commands from C<ALL> using the '!' operator. A user can trivially circumvent this by copying the desired command to a different name and then executing that. For example: bill ALL = ALL, !SU, !SHELLS Doesn't really prevent B<bill> from running the commands listed in I<SU> or I<SHELLS> since he can simply copy those commands to a different name, or use a shell escape from an editor or other program. Therefore, these kind of restrictions should be considered advisory at best (and reinforced by policy). =head1 PREVENTING SHELL ESCAPES Once B<sudo> executes a program, that program is free to do whatever it pleases, including run other programs. This can be a security issue since it is not uncommon for a program to allow shell escapes, which lets a user bypass B<sudo>'s access control and logging. Common programs that permit shell escapes include shells (obviously), editors, paginators, mail and terminal programs. There are two basic approaches to this problem: =over 10 =item restrict Avoid giving users access to commands that allow the user to run arbitrary commands. Many editors have a restricted mode where shell escapes are disabled, though B<sudoedit> is a better solution to running editors via B<sudo>. Due to the large number of programs that offer shell escapes, restricting users to the set of programs that do not if often unworkable. =item noexec Many systems that support shared libraries have the ability to override default library functions by pointing an environment variable (usually C<LD_PRELOAD>) to an alternate shared library. On such systems, B<sudo>'s I<noexec> functionality can be used to prevent a program run by B<sudo> from executing any other programs. Note, however, that this applies only to native dynamically-linked executables. Statically-linked executables and foreign executables running under binary emulation are not affected. To tell whether or not B<sudo> supports I<noexec>, you can run the following as root: sudo -V | grep "dummy exec" If the resulting output contains a line that begins with: File containing dummy exec functions: then B<sudo> may be able to replace the exec family of functions in the standard library with its own that simply return an error. Unfortunately, there is no foolproof way to know whether or not I<noexec> will work at compile-time. I<noexec> should work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX 11.x. It is known B<not> to work on AIX and UnixWare. I<noexec> is expected to work on most operating systems that support the C<LD_PRELOAD> environment variable. Check your operating system's manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see if C<LD_PRELOAD> is supported. To enable I<noexec> for a command, use the C<NOEXEC> tag as documented in the User Specification section above. Here is that example again: aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi This allows user B<aaron> to run F</usr/bin/more> and F</usr/bin/vi> with I<noexec> enabled. This will prevent those two commands from executing other commands (such as a shell). If you are unsure whether or not your system is capable of supporting I<noexec> you can always just try it out and see if it works. =back Note that restricting shell escapes is not a panacea. Programs running as root are still capable of many potentially hazardous operations (such as changing or overwriting files) that could lead to unintended privilege escalation. In the specific case of an editor, a safer approach is to give the user permission to run B<sudoedit>. =head1 SEE ALSO L<rsh(1)>, L<su(1)>, L<fnmatch(3)>, L<sudo(8)>, L<visudo(8)> =head1 CAVEATS The I<sudoers> file should B<always> be edited by the B<visudo> command which locks the file and does grammatical checking. It is imperative that I<sudoers> be free of syntax errors since B<sudo> will not run with a syntactically incorrect I<sudoers> file. When using netgroups of machines (as opposed to users), if you store fully qualified hostnames in the netgroup (as is usually the case), you either need to have the machine's hostname be fully qualified as returned by the C<hostname> command or use the I<fqdn> option in I<sudoers>. =head1 BUGS If you feel you have found a bug in B<sudo>, please submit a bug report at http://www.sudo.ws/sudo/bugs/ =head1 SUPPORT Limited free support is available via the sudo-users mailing list, see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives. =head1 DISCLAIMER B<sudo> is provided ``AS IS'' and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distributed with B<sudo> or http://www.sudo.ws/sudo/license.html for complete details.